Polyester such as polyethylene terephthalate has been widely used as a fiber, a film, a resin, or the like because of its excellent characteristics. Effective utilization of polyester remnants in the form of a fiber, a film, or the like, produced in the production process thereof is not only important for reducing the cost of the products but also a large problem regarding the environment. As the disposal methods therefor, various proposals by material recycle, thermal recycle, and chemical recycle have been made. Out of these, with the material recycle, for polyester resin remnants of PET bottles, and the like, PET bottles are recovered, and positive reuse thereof are carried out by municipalities acting as the centers. However, to fiber remnants, this recycle method has been very difficult to apply.
Whereas, the thermal recycle for converting polyester wastes into fuel has a feature of reuse of the heat of combustion of polyester wastes. However, the heat value per unit weight of polyester is relatively low. Therefore, large heat generation cannot be effected unless a large quantity of polyester wastes are burned. Accordingly, there is a problem that the polyester raw material is not effectively utilized, which is not preferable from the viewpoint of the conservation of natural resources. In contrast, with the chemical recycle, polyester wastes are recycled into polyester raw materials. For this reason, the degradation of quality caused by recycling less occurs, and the recycle is excellent as recycle of a closed loop. This closed loop represents a loop going through one cycle of from polyester raw materials, polyester fiber products, consumption by users, recovery of used polyester products, and recycle factories of polyester products, and back to polyester materials.
With the chemical recycle, the recycling is mostly targeted for resin remnants and film remnants. As the methods for recycling polyester fiber remnants, for example, considering based on polyethylene terephthalate which is typical polyester, JP-A-48-61447 discloses the following method, and other methods: polyester remnants are depolymerized with an excess of ethylene glycol (which may be hereinafter abbreviated as EG), and then, the resulting bis-β-hydroxy ethylene terephthalate is directly polycondensed to obtain regenerated polyester. However, with this method, in the depolymerization reaction step, polyester remnants and EG are charged both together in a depolymerization reaction tank for depolymerization. Therefore, in some cases, the charged polyester remnants may form agglomerates inside the reaction tank, which makes stirring impossible. For this reason, unfavorably, the inside of the depolymerization reaction tank becomes ununiform, and the depolymerization time becomes longer. Further, with this method, the amount of EG to be used for depolymerization is large. This unfavorably results in not only economical disadvantages, but also the formation of impurities such as diethylene glycol in depolymerization. This also results in the following defects: the physical properties of the resulting polyethylene terephthalate, particularly, the softening point thereof is remarkably deteriorated, and only polyethylene terephthalate (which may be hereinafter abbreviated as PET) low in physical properties can be obtained. Thus, in the related art, the technology for efficiently disposing of polyester fiber remnants has not been completed yet.
Polyester, for example, polyalkylene terephthalate, particularly, PET is produced in large amounts for use in fibers, films, beverage bottles, other resin formed products, or the like because of its excellent chemical stability.
However, the disposal of wastes of fibers, films, bottles, or other resin products, or PET of nonstandard products generated in large amounts with the increase in production and usage is currently becoming a large social issue. Under such circumstances, regarding the material recycle, the chemical recycle, the thermal recycle, or the like, various proposals have been made on the recycling methods.
On the other hand, out of the wastes, particularly, disposal of PET bottles is becoming even more serious due to the bulkiness. However, as the recycling method, only recycling of such a degree as to melt the recovered used PET bottles again into fiber is carried out as the material recycle. When merely the recovered used PET bottles are melt molded to manufacture bottles, it is impossible to use the bottles as PET bottles again due to the reduction of the physical properties.
Whereas, for the reuse method in which PET bottles are washed, and filled again, the method cannot be a permanent measure from the viewpoints of the payer of recycling cost, the safety, and the hygiene, and because of the facts that there is a limit on the number of reuses, and that the bottles end up by being disposed of, and other facts. Further, PET bottle remnants may include therein different types of plastics such as polystyrene (which may be hereinafter abbreviated as PS), polypropylene (which may be hereinafter abbreviated as PP), polyethylene (which may be hereinafter abbreviated as PE), polyvinyl chloride (which may be hereinafter abbreviated as PVC), or other polyolefin resins derived from components of PET bottles such as labels, shrink films, base cups, or caps, aluminum derived from aluminum cans, iron derived from steel cans, adhesives, pigments, dyes, or the like.
Also to separately recovered PET bottle bales (compressed and baled PET bottles), mixing of foreign matter materials is difficult to avoid. Also, in the chemical recycle in which decomposition into monomers forming PET is carried out by the use of water or a solvent such as methanol (which may be hereinafter abbreviated as MeOH) or EG for reuse, in the process of the heating operation or the reaction operation, foreign matter materials may generate various decomposed gases (e.g., hydrogen chloride gas) and various decomposed products (e.g., lower hydrocarbon), or the mixed matters themselves may remarkably reduce the purity of the recovered dimethyl terephthalate (which may be hereinafter abbreviated as DMT). Alternatively, various decomposed products may be molten and solidified in the recovery apparatus to damage the devices.
Examples of the chemical recycle may include: the method described in JP-A-11-21374, in which polyester wastes are hydrolyzed in the presence of an alkali compound to obtain terephthalic acid (which may be hereinafter abbreviated as TA), and the method described in U.S. Pat. No. 5,952,520 in which DMT and EG are obtained by vapor phase MeOH decomposition in MeOH.
However, all of these require the reaction conditions of high temperatures of 200° C. or more. For this reason, when different types of plastics which start to decompose from 190° C. as PVC are mixed, the temperature range of the operation of carrying out chemical recycle is unfavorably restricted.
Further, in JP-A-2000-169623, the following process is proposed: PET wastes are decomposed with EG, and the resulting bis-β-hydroxy ethyl terephthalate (which may be hereinafter abbreviated as BHET) is purified by a thin film evaporation apparatus; and then, BHET is melt polycondensed to obtain PET. Also in this case, there is a step of applying a heat history of 200° C. or more. Thus, when a different type of plastic which tends to undergo thermal decomposition such as PVC is mixed, it is not possible to obtain PET with favorable physical properties.
Namely, in the chemical recycle, the impurity content of such a degree as not to cause a problem is higher than with the material recycle. However, in the pretreatment step, foreign matters are required to be removed almost completely. Whereas, it is generally known that PET for bottles is obtained in the following manner: by using DMT or TA, and EG as starting materials, oligomers are obtained by the ester interchange reaction or the esterification reaction, followed by the polycondensation reaction. Unless the DMT or TA of the raw material is not the highly purified one sufficiently low in impurity content, the resulting PET cannot be used for PET bottles.
Due to the circumstances in which there are various such restrictions, there has been no method in which the effective components of used PET bottles are recovered to obtain PET for PET bottles again with the chemical recycle process.
Whereas, when polyester fibers are targeted for recovery, mixing of polyester fibers containing a dye may be unavoidable. The dye contained in the dyed polyester fibers undergoes thermal decomposition during a series of reactions such as depolymerization at high temperatures in the presence of a catalyst. The thermally decomposed products are dispersed in the recovered useful components, and remarkably degrade the quality of the recovered useful components. As an example of the method in which such problems are mentioned, and countermeasures are taken, mention may be made of the method described in JP-A-2004-217781. However, the number of methods disclosed heretofore is small. Further, the methods are not capable of achieving a sufficient recovery efficiency.